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What is a 'Sandbank': A Commentary Based on a
Maltese Case Study
Leyla Knittweis(1), Julian Evans(1,2), Ricardo Aguilar(3), Helena
Alvarez(3,4), Joseph A. Borg(1,5), Silvia Garcia(3,6), Patrick J.
Schembri(1,7)
(1) Department of Biology, Faculty of Science, University of Malta, Msida,
MSD 2080. Tel No: +356 23402850
Email: leyla.knittweis@um.edu.mt
(2) Email: julian.evans@um.edu.mt
(3) Fundacion Oceana, Gran Via 59, 28013 Madrid, Spain. Tel No: +34 911
440880
Email: raguilar@oceana.org
(4) Email: halvarez@oceana.org
(5) Email: joseph.a.borg@um.edu.mt
(6) Email: sgarcia@oceana.org
(7) Email: patrick.j.schembri@um.edu.mt
Abstract
Habitat Type 1110 ‘Sandbanks which are slightly covered by sea water all the
time’, listed in Annex I of the EU’s Habitats Directive, is defined in the EU ‘Habitat
Interpretation Manual’ as "elevated, elongated, rounded or irregular topographic features,
permanently submerged and predominantly surrounded by deeper water", which "consist
mainly of sandy sediments", and where the water depth above the sandbank "is seldom
more than 20 m below chart datum". It is specified that Mediterranean sandbanks may be
characterised by the marine angiosperm Cymodocea nodosa, but also that "on many
sandbanks macrophytes do not occur".
The main objective of the present work was to characterise ‘geomorphological’
sandbanks around the Maltese Islands. Information on the physical characteristics of
This is a pre-print of an article that was published in the MEDCOAST 2017 conference
proceedings. The final version of the article was published as:
Knittweis L., Evans J., Aguilar R., Alvarez H., Borg J.A., Garcia S. and Schembri P.J. (2017).
What is a ‘sandbank’? A commentary based on a Maltese case study. In: Özhan E. (ed.)
Proceedings of the thirteenth International MEDCOAST Congress on Coastal and Marine
Sciences, Engineering, Management and Conservation, Malta, 31 October - 4 November
2017, p.405–414.
sandy elevations in Għajn Tuffieħa, Mellieħa Bay, and the Comino Blue Lagoon was
collected during the LIFE BaĦAR for N2K project surveys in 2016, while biotic data
from the Għajn Tuffieħa and Mellieħa Bay banks was collected in 2013 as part of an
ecological survey commissioned by the then Malta Environment and Planning Authority.
The results of these studies indicate that sandbanks in the Maltese Islands tend to
be present in very shallow waters, at depths ranging from ca. 0.02 m to 2.00 m. The
surveyed sandbanks had variable dimensions, with lengths ranging from ca. 11 m to 180
m, and widths ranging from ca. 1.5 m to 17 m. Samples of infauna collected using core
samples in 2013 did not reveal any significant differences in the total number of species
or in the total abundance of organisms between the sandbanks and nearby reference sites.
No macroflora, and thus no C. nodosa, were recorded on any of the surveyed sandbanks.
In the Maltese Islands, associations with C. nodosa are in fact found throughout the
infralittoral, down to ca. 45 m. Cymodocea nodosa may occur as a dense meadow or very
sparsely, either as almost monospecific stands or in association with other seagrasses
(Posidonia oceanica or Halophila stipulacea) and/or macroalgae (e.g. Caulerpa
cylindracea or Caulerpa prolifera). Cymodocea nodosa is thus clearly not limited to the
environmental conditions created by sandbanks in the Maltese Islands, is not generally
present where such conditions occur, and is therefore not a useful indicator species for
this habitat type.
Detailed seasonal studies of physical characteristics are required to confirm with
certainty that the habitats identified in Malta are indeed true sandbanks in the
geomorphological sense. Monitoring of benthic assemblages is also required to ascertain
whether there are any biotic assemblages which could serve as biological indicators for
this habitat type, and to demonstrate the ecological importance of this habitat.
Introduction
Sandbanks are found in coastal and shelf areas, where currents act in conjunction
with coastal or seabed topography to move and accumulate mobile sediments in a wide
variety of forms (Dyer and Huntley, 1999; Kaiser et al, 2004). Dyer and Huntley (1999)
developed a descriptive classification scheme to harmonise the definitions used by marine
geologists and physical oceanographers, and considered formation processes as well as
the hydrodynamic setting to be key factors influencing the long-term development of
sandbanks. As a result of their unique physical characteristics, sandbanks may hold their
own distinct assemblage of flora and fauna adapted to the conditions of this habitat
(Withers and Thorp, 1978; Kaiser et al., 2004; Ellis et al., 2011; Atalah et al., 2013;
Markert et al., 2015). Sandbanks are of considerable importance in stabilising coastlines
and preventing erosion, and may act as nursery grounds for a number of commercially
exploited species of fish in Northern Europe (Dyer and Huntley, 1999; Atalah et al.,
2013).
In recognition of the known importance of sandbank habitats in Northern Europe,
the European Union’s (EU) Habitats Directive (HD; Council Directive 92/43/EEC) lists
'Habitat Type 1110 - Sandbanks which are slightly covered by seawater all the time' in
Annex I, as a 'natural habitat type of community interest whose conservation requires the
designation of special areas of conservation'. The EU ‘Habitat Interpretation Manual’
(EC, 2013), defines sandbank habitats as "elevated, elongated, rounded or irregular
topographic features, permanently submerged and predominantly surrounded by deeper
water", which "consist mainly of sandy sediments", although "larger grain sizes,
including boulders and cobbles, or smaller grain sizes including mud may also be
present". It is specified that ‘slightly covered by sea water all the time’ refers to sandbanks
in which the water depth is seldom more than 20 m below chart datum. In a separate
section on ‘plants’ associated with this habitat, the Interpretation Manual specifies that in
the Mediterranean "the marine angiosperm Cymodocea nodosa, together with photophilic
species of epiphytes (more than 15 species, mainly small red algae of the Ceramiaceae
family), associated with Posidonia beds" may be found on sandbanks, but that "on many
sandbanks macrophytes do not occur".
With regards to the different classification schemes currently in use for the
description, designation and mapping of habitats in Europe, the EU Habitat Interpretation
Manual considers that categories corresponding to sandbanks can be the relevant types
within the EUNIS categories 'A5.1 Sublittoral coarse sediment'; 'A5.2 Sublittoral sand';
'A5.4 Sublittoral mixed sediments'; and 'A5.5 Sublittoral macrophyte-dominated
sediment'; the manual also lists the habitat classes relevant to sandbanks included in the
RAC-SPA system. The EUNIS and the RAC-SPA systems include habitat categories
which refer to ‘associations with Cymodocea nodosa on well-sorted fine sands’ and
‘associations with Cymodocea nodosa on superficially muddy sands in sheltered waters’,
These, and other habitat categories, would however only be applicable to sandbanks in
the presence of elevated, elongated, rounded or irregular topographic features surrounded
by deeper waters, i.e. where sandbanks in the geomorphological sense are present.
Despite the above considerations several Mediterranean Member States consider
C. nodosa beds on sand as equivalent to the HD Annex I sandbank habitats, since the EU
Interpretation Manual (EC, 2013) lists C. nodosa as a characteristic plant species of
sandbanks. Member States adopted this interpretation since they consider that the current
definition of sandbanks given in the EU Habitat Interpretation Manual is based on
sandbanks from Northern Europe (Evans et al., 2014).
In the Maltese Islands several areas with C. nodosa on sand are present in the
marine Sites of Community Importance (SCIs) declared under the Habitats Directive.
Very limited information is however available on sandbank habitats in the Maltese
Islands; while sandy bedforms with a raised topography exist in shallow waters around
the Maltese Islands, it is not known if these are ‘sandbanks’ in the geomorphological
sense since there is no information on the processes that form and maintain them. In this
context, the main objectives of the present work were to investigate the physical
characteristics of ‘geomorphological’ sandbanks in the Maltese Islands, and to interpret
the results in light of the biotic assemblages found on such sandy elevations.
Material and Methods
In order to locate sandy elevations SCUBA dives were carried out in areas where
sandbanks in the geomorphological sense were considered likely to be present, as part of
the LIFE BaĦAR for N2K project surveys in 2016. Concurrently, snorkelers surveyed
shallow areas (Fig. 1). Sandy elevations that might be described as ‘sandbanks’ were
located at Għajn Tuffieħa, Mellieħa Bay, and the Comino Blue Lagoon (Fig. 1). The
approximate physical dimensions of the sandbanks, the bathymetry of the surrounding
seabed, as well as their precise locations were subsequently recorded using measuring
tapes and a handheld GPS. In addition the presence or absence of submerged vegetation
on the sandy elevations was noted.
Fig. 1: Location of areas surveyed for sandbanks and sandbanks for which physical
characteristics were measured during the 2016 LIFE BaĦAR for N2K project
surveys.
Information on the biotic assemblages present on the Għajn Tuffieħa and Mellieħa
Bay sandbanks was available from a survey commissioned by the then Malta
Environment Planning Authority (MEPA) in 2013. This survey entailed the collection of
sediment cores in order to characterise the infauna present. Three replicate sediment core
samples (using 10 cm diameter X 12 cm height corers) were collected from each of two
stations on each sandbank, and from two nearby reference stations in waters that did not
have largely different water depths to avoid any potential influence of this factor. Samples
were fixed and preserved in 10% formaldehyde upon arrival at the laboratory.
In the laboratory, the samples were washed to remove the fine sediment (<0.5 mm
fraction) and the preservative and were then sorted to separate out all macrofauna
(animals larger than 0.5 mm). The motile macrofauna were then identified to the lowest
possible taxon and counted. Where identification to species level was not possible, the
different species present were labelled using an alphabetical code (e.g. Paraonidae sp. A,
Paraonidae sp. B, etc.). Estimates of the total number of species and the total abundance
were then made for each replicate core sample.
Three-factor Analysis of Variance (ANOVA), with α set at 0.05 was used to test
for significant differences in the total abundance and species richness of biota recorded
from the samples. The factors used were ‘Locality’ (2 levels) ‘Habitat Type’ (2 levels)
and ‘Station’ (nested within ‘Habitat Type’ and ‘Locality’). Prior to analyses, the data
were checked for normality and homogeneity of variances by using Cochran’s test and,
where necessary, an appropriate transformation was carried out. All statistical tests were
implemented using the ANOVA computer programme GMAV5 developed at the
University of Sydney.
Results and Discussion
The information collected during the present study indicates that raised sandy
elevations tend to be present in very shallow waters in the Maltese Islands, with the
highest part of the surveyed sandbanks at depths ranging from 0.02 m to 2 m, and the
depth of the surrounding seabed from 0.2 - 2.6 m. The physical dimensions of the three
sandbanks surveyed in 2016 were variable, with the lengths of sandy elevations ranging
from 11 m to 180 m, and widths ranging from 1.5 m to 17 m. In all cases the surveyed
sandbanks were more or less consistent with part of the description of Habitat 1110 in the
Interpretation Manual of European Union habitats in in that the banks consisted of
submerged sandy sediments that are elevated and elongated, and surrounded by deeper
water. However, the habitat description in the Interpretation Manual is very broad and
lacks any quantitative measure of precisely how 'elevated' a feature surrounded by deeper
water should be in order to be classed as a sandbank; the crests of the sandy elevations
measured during the present study were a mere 18 cm higher than the surrounding deeper
waters. Moreover, detailed geomorphological, and ideally hydrological, studies which
span different seasons over several years would be required in order to understand the
processes which maintain these sandbank-like features, and to see whether the surveyed
sandy elevations indeed persistently have structures in line with the descriptions of
sandbanks in the geomorphological literature.
No macroflora or megafauna were recorded at any of the surveyed sandbanks.
Infauna present on sandbanks was dominated by polychaetes. Table 1 gives a species-
sample matrix showing the total number of macrobenthic invertebrates recorded in the
sediment cores collected from the two sandbanks and nearby reference sampling stations
during the 2013 survey.
Table 1: Species-sample matrix showing the total number of macrobenthic invertebrates
recorded in sediment cores taken at sampling stations located on (stations 1, 2)
and off (stations 3, 4) the sandbanks at Għajn Tuffieħa Bay and Mellieħa Bay.
Għajn Tuffieħa Bay
Mellieħa Bay
On
Sandbank
Reference
Station
On
Sandbank
Reference
Station
Phylum
Species
St. 1
St. 2
St. 3
St. 4
St. 1
St. 2
St. 3
St. 4
Crustacea
Bathyporeia sp.
1
1
Monoculodes sp.
1
Mollusca
Donax venustus
1
1
Loripes orbiculatus
10
1
Polychaeta
Capitellidae sp.
1
2
Orbiniidae sp.
24
47
2
12
1
Paraonidae sp. A
5
1
2
Paraonidae sp. B
2
Spionidae sp.
10
15
2
3
The overall mean total number of species per core was 2.5 on the sandbank and 3.3 off
the sandbank at Għajn Tuffieħa Bay, and 0.3 on the sandbank and 0.3 off the sandbank at
Mellieħa Bay. The overall mean total abundance per core was 17.2 on the sandbank and
6.3 off the sandbank at Għajn Tuffieħa Bay, and 0.3 on the sandbank and 0.3 off the
sandbank at Mellieħa Bay (Fig. 2 and 3). The results of the three-factor ANOVA indicated
that the difference in the total number of species between the two localities was significant
(ANOVA; p<0.01). Similarly the difference in the total abundance of individuals
recorded from the two localities was significant (ANOVA; p<0.001). No significant
differences were indicated by the ANOVA between the sandbank habitat and the
reference stations, although the mean total abundance of individuals found on sandbanks
and at nearby reference stations varied at Għajn Tuffieħa Bay (Fig. 3).
Fig. 2: Mean species richness ± 1 standard deviation per core recorded from stations
located on (stations 1 and 2, marked in light grey) and off (stations 3 and 4, marked
in dark grey) the sandbanks at Għajn Tuffieħa Bay and Mellieħa Bay during the
2013 survey.
Fig. 3: Mean total abundance ± 1 standard deviation per core recorded from stations
located on (stations 1 and 2, marked in light grey) and off (stations 3 and 4, marked
in dark grey) the sandbanks located at Għajn Tuffieħa Bay and Mellieħa Bay
during the 2013 survey.
0
1
2
3
4
5
1 2 3 4
Mean Species
Richness per Core
Station Number
Għajn Tuffieha Bay
0
1
2
3
4
5
1 2 3 4
Mean Species
Richness per Core
Station Number
Mellieħa Bay
0
5
10
15
20
25
30
1 2 3 4
Mean Total
Abundance per Core
Station Number
Għajn Tuffieha Bay
0
5
10
15
20
25
30
1 2 3 4
Mean Total
Abundance per Core
Station Number
Mellieħa Bay
A possible reason for the low number of species and low number of individuals
recorded at Mellieħa Bay compared to Għajn Tuffieħa Bay is the higher anthropogenic
impact at the former site, further exacerbated by the fact that the sandbank at Mellieħa
Bay was located in shallower waters more likely to be impacted by trampling. However,
if the two sandbanks are maintained by hydrodynamism coupled with coastal morphology
and sand supply, any or all of these factors, as well as the relative contribution of each
may be different for the two bays.
No macroflora, and thus no C. nodosa, was recorded at the sampling stations on
the sandbanks surveyed in 2013, and no submerged vegetation was present on the
sandbanks surveyed in 2016. This confirms that ‘on many sandbanks macrophytes do not
occur’ as stated in the EU Habitat Interpretation Manual (EC, 2013). Whilst macroflora
such as C. nodosa may occur on other sandbanks in the Maltese Islands, it is not correct
to base a definition of sandbanks solely on the associated vegetation, at least in the case
of the Maltese Islands. Cymodocea nodosa is a fast growing and tolerant, species which
can withstand a variety of environmental conditions and as a consequence is widely
distributed in Mediterranean coastal waters, including in high-energy and degraded
environments where P. oceanica meadows are not able to thrive (Marba and Duarte,
1995; Delgado et al., 1997; Lardi et al., 2015). It can co-occur with other seagrasses in
mixed meadows, and has been observed to grow in association with opportunistic
macroalgae (Olesen et al., 2002; Orfanidis et al., 2009; Sghaier et al., 2011; Pérez-Ruzafa
et al., 2012; Lardi et al., 2015). Indeed, in the Maltese Islands, associations with the
seagrass C. nodosa are found throughout the infralittoral, from very shallow depths down
to about 45 m (GAS and MEPA, 2003). Locally C. nodosa has been observed to occur as
dense meadows or very sparsely, and the plant may occur both as monospecific stands or
in association with the seagrasses P. oceanica and Halophila stipulacea, and/or
macroalgae such as Caulerpa cylindracea or Caulerpa prolifera (Borg and Schembi,
1995; Pirotta and Schembri, 1997; GAS and MEPA, 2003; Borg et al., 2013). Cymodocea
nodosa is thus clearly not limited to the environmental conditions created by sandbanks,
and is thus not a useful indicator species for this habitat type.
Conclusion
In the Maltese Islands, sandbanks generally consistent with the physical
description of Habitat 1110 given in the EU Habitat Interpretation Manual (EC, 2013)
were recorded in very shallow waters at several locations during two surveys carried out
in 2013 and 2016. The banks consisted of sandy sediments, were elevated and elongated,
permanently submerged, and surrounded by deeper water.
The results of a preliminary assessment of infauna present on sandbanks and at
nearby reference stations did not find any significant differences with regards to the total
number of species or the total abundance of polychaetes, bivalves and amphipods present.
Moreover, no macroflora, and thus no C. nodosa, was recorded on any of the surveyed
sandbanks. The results of the infauna assemblages need to be interpreted with caution due
to the low number of samples and replicates collected. On the other hand, the authors are
of the opinion that it can be concluded with certainty that C. nodosa is not a useful
indicator species for sandbank habitats in the Maltese Islands. This species is in fact
widely distributed and able to grow under a variety of environmental conditions in Malta
and throughout the Mediterranean (Borg and Schembri, 1995; GAS and MEPA, 2003;
Borg et al., 2013; Lardi et al., 2015), and is thus not limited to the environmental
conditions created by sandbanks. The results of the present study consequently show that
considering C. nodosa beds to be equivalent to the HD Annex I sandbank habitats, as is
currently the interpretation of several Mediterranean Member States (Evans et al., 2014),
is not appropriate.
Detailed seasonal studies of physical characteristics are required to confirm that
the features identified in the present study are indeed true sandbanks in the
geomorphological sense. Monitoring of benthic assemblages is also required to ascertain
whether there are any biotic assemblages which could serve as biological indicators for
this habitat type and to characterise seasonal changes. Moreover, the actual ecological
importance of this habitat, and thus the relevance of protecting such habitats in the
Maltese Islands, and indeed in the Mediterranean Sea more generally, has yet to be
ascertained.
Acknowledgements
The LIFE BaĦAR for N2K (LIFE12 NAT/MT/000845) Project is 50%
cofinanced by the EU LIFE+ Funding Programme and implemented by the Environment
and Resources Authority (ERA), the University of Malta, Fundación Oceana, the Ministry
for the Environment, Sustainable Development, and Climate Change (MESDC), and the
Department for Fisheries and Aquaculture within MESDC. We thank the ERA and the
Ministry for Transport and Infrastructure - Continental Shelf Department for granting the
permits to undertake this work.
References
Atalah, J., Fitch, J., Coughlan, J., Chopelet, J., Coscia, I. and Farrell, E. (2013), “Diversity
of demersal and megafaunal assemblages inhabiting sandbanks of the Irish Sea”,
Marine Biodiversity, 43(2), 121-132.
Dyer, K.R. and Huntley, D.A. (1999), “The origin, classification and modelling of sand
banks and ridges”, Continental Shelf Research, 19(10), 1285-1330.
Borg, J.A. and Schembri, P.J. (1995), “Epibenthic macrofaunal assemblages and bottom
heterogeneity in the shallow infralittoral of the Maltese Islands”, Rapports
Commission International pour l'Exploration Scientifique de la Mer
Mediterranée, 34, 20.
Borg, J.A., Knittweis, L. and Schembri, P.J. (2013), “Compilation of an interpretation
manual for marine habitats within the 25 NM Fisheries Management Zone around
the Republic of Malta [MEPA tender reference: T2/2013]”. Ecoserv Ltd. Report,
Mosta, Malta, 218 p.
Delgado, O., Grau, A., Pou, S., Riera, F., Massuti, C., Zabala, M. and Ballesteros, E.
(1997), “Seagrass regression caused by fish cultures in Fornells Bay (Menorca,
Western Mediterranean)”, Oceanologica Acta, 20, 557–563.
EC [European Commission] (2013), “Natura 2000 Interpretation Manual of European
Union Habitats – EUR28”, European Commission Directorate General for the
Environment (DG ENV), Nature ENV B.3. Report, 146 p.
Ellis, J.R., Maxwell, T., Schratzberger, M. and Rogers, S.I. (2011), “The benthos and fish
of offshore sandbank habitats in the southern North Sea”. Journal of the Marine
Biological Association of the United Kingdom, 91(6), 1319-1335.
Evans, D., Condé, S. and Royo Gelabert, E. (2014), “Crosswalks between European
marine habitat typologies - A contribution to the MAES marine pilot”, ETC/BD
Report for the EEA, 29 p.
GAS [Geological Assistance and Services] and MEPA [Malta Environment and Planning
Authority] (2003), “Baseline survey of the extent and character of Posidonia
oceanica (L.) Delile meadows in the territorial waters of the Maltese islands”.
Unpublished Geological Assistance and Services SRL Report [IDP GAS:
PAM001], Bologna, Italy, 240 p.
Kaiser, M.J., Bergmann, M., Hinz, H., Galanidi, M., Shucksmith, R., Rees, E.I.S.,
Darbyshire, T. and K. Ramsay (2004), “Demersal fish and epifauna associated
with sandbank habitats”, Estuarine, Coastal and Shelf Science, 60(3), 445-456.
Lardi, P., Gerakaris, V., Panayotidis, P., Danielidis, D.B. and Economou-Amilli, A.
(2016), “Study of the morphological and structural features of the seagrass
Cymodocea nodosa (Ucria) Ascherson in an embayment of the Aegean Sea
(Saronikos Gulf, Greece)”, In: Proceedings of the Eleventh Panhellenic
Symposium on Oceanography and Fisheries, 13-17 May, Mytilene, Lesvos
Island, Greece, 477-480.
Marba, N. and Duarte, C.M. (1995), “Coupling of seagrass (Cymodocea nodosa) patch
dynamics to subaqueous dune migration”, Journal of Ecology, 381-389.
Markert, E., Kröncke, I. and Kubicki, A. (2015), “Small scale morphodynamics of
shoreface-connected ridges and their impact on benthic macrofauna”, Journal of
Sea Research, 99, 47-55.
Olesen, B., Enríquez, S., Duarte, C.M. and Sand-Jensen, K. (2002), “Depth-acclimation
of photosynthesis, morphology and demography of Posidonia oceanica and
Cymodocea nodosa in the Spanish Mediterranean Sea”, Marine Ecology Progress
Series, 236, 89-97.
Orfanidis, S., Papathanasiou, V., Gounaris, S. and Theodosiou, T. (2009), “Size
distribution approaches for monitoring and conservation of coastal Cymodocea
habitats”, Aquatic Conservation: Marine and Freshwater Ecosystems, 20, 177-
188.
Pérez-Ruzafa, A., Marcos, C., Bernal, C.M., Quintino, V., Freitas, R., Rodrigues, A.M.,
García-Sánchez, M. and Pérez-Ruzafa, I.M., (2012), “Cymodocea nodosa vs.
Caulerpa prolifera: Causes and consequences of a long term history of interaction
in macrophyte meadows in the Mar Menor coastal lagoon (Spain, southwestern
Mediterranean)”, Estuarine, Coastal and Shelf Science, 110, 101-115.
Pirotta, K. and Schembri, P.J. (1997), “Characterization of the major marine biotopes of
the soft substrata around the Maltese Islands”, In: Özhan, E. (Ed.), Proceedings
of the Third International Conference on the Mediterranean Coastal Environment
MEDCOAST 97, 11-14 November, Qawra, Malta, 25-37.
Sghaier, Y.M., Zakhama-Sraieb, R. and Charfi-Cheikbraiha, F. (2014), “Effects of the
invasive seagrass Halophila stipulacea on the native seagrass Cymodocea
nodosa”, In:. Proceedings of the Fifth Mediterranean Symposium on Marine
Vegetation, 27-28 October, Portorož, Slovenia, 167-171.
Withers, R.G. and Thorp, C. H. (1978), “The macrobenthos inhabiting sandbanks in
Langstone Harbour, Hampshire”, Journal of Natural History, 12(4), 445-455.
